Combustion chamber with fuel vaporizer



Feb. 19, 1957 F. G. DOUGHERTY COMBUSTION CHAMBER WITH FUEL VAPORIZERFiled Dec. 15, 1950 H y i a w y w l W W Z A g .u... w. MM w 1 W y.\\\\..n y a W Gltoruegs 2,781,637 Patented Feb. 19, 1957 COMBUSTIONCHAMBER WITH FUEL VAPORIZER Floyd G. Dougherty, Indianapolis, Ind.,assignor to General Motors Corporation, Detroit, Mich, a corporation ofDelaware Application December 15, 1950, Serial No. 200,965 7 Claims.(Cl. 60--39.71)

My invention relates to combustion apparatus, particularly to combustionchambers for gas turbine engines. The primary object of the invention isto improve combustion in such engines, especially aircraft engines whichoperate at high altitudes.

Maintenance of proper combustion conditions in aircraft gas turbines isdifiicult, but great progress has been made in this respect in recentyears. At sea level or low altitudes, with fairly volatile fuels, nogreat difficulty is now experienced. It is found, however, thatcombustion becomes more critical as altitude is increased, untilultimately an altitude is attained at which combustion cannot beconsistently maintained. Also, reignition of the flame is usuallyimpossible through a considerable altitude range immediately below theceiling.

The highest possible ceiling, and good performance up to the ceiling,are important requirements in certain types of aircraft.

My invention is adapted to increase the operational ceilings of gasturbine engines by several thousand feet, to provide more consistentperformance, and to permit the elimination of high pressure fuel systemsand liquid fuel spray nozzles with their attendant shortcomings.

Other advantages of the invention are that it makes possible the use ofshorter burners, thus permit-ting a reduction in the length and weightof the engine; improves combustion efficiency as a result ofbetterfuel-air mixing and better temperature distribution in the burner;lessens pressure drop in the combustion section; and improves ignitionand blowout characteristics.

The invention involves a novel arrangement for introduction of air forcombustion and mixing of fuel in a vaporized condition with the air inconnection with a fuel vaporizer in each combustion chamber where liquidfuel is used.

Many ignition and combustion problems arising from jet engine burnerdevelopment are directly related to the inability of the burner toconsume liquid fuels most effectively. When the fuel is admitted in theform of a spray, as with the conventional spray nozzle, the fuel mustfirst be broken into fine particles, distributed throughout thecombustion chamber, heated, vaporized, and mixed with air beforeignition and combustion can occur. This not only creates a time lag inthe ignition sequence, but also requires the fuel to be introduced underunduly high pressure. This necessitates burner designs that purposelypromote turbulence and pressure losses that are detrimental to overallengine performance.

The principal objects of the invention are to improve combustion in gasturbine engines, to improve high-altitude performance, to facilitate theuse of less volatile fuels than are now preferred, to provide animproved combustion chamber, to provide a more satisfactory fuel system,and to provide an improved vaporizer and fuel injection apparatus.

The appended detailed description of the preferred embodiment of theinvention will make clear to those skilled in the art the advantages ofthe invention and the pre-' ferred manner in which the objects arerealized.

Referring to the drawings: Figure l is a partial longitudinal sectionalview of a gas turbine combustion chamber incorporating the invention,and Figures 2 and 3 are partial cross-sectional views taken on theplanes indicated in Figure 1.

. In the interest of conciseness, I refrain from illustrating ordescribing a gas turbine engine as a whole, since such- =engines arewell known to those skilled in the art, and the details of the turbine,the compressor, various auxiliarycomponents, and the organizationthereof into an engine are immaterial to my invention. Since theinvention may be employed in combustion chambers of varying structure, Ihaveshown only so much of an illustrative combustion apparatus as isrequisite to make the invention clear to those skilled in the art.

In Figure 1, the diffuser 11 of the compressor of a gas turbine engineis represented as bounded by inner and outer walls 12 and 13. Thispassage may be annular, as is customary with axial-flow compressors, ormay be one of a plurality of outlets of a radial-flow compressor. If thediffuser is for an axial-flow compressor, it is ordinarily divided byradial partitions into a number of individual outlets arrangedcircumferentially around the axis of the compressor shaft. At eachoutlet of the diffuser a flanged ring 14 is mounted. The ring 14constitutes a pilot for a ring 16 fixed to theforward end of a generallycylindrical sheet metal shell 17 which constitutes a combustion chamberof the engine. The combustion chamber 17 is assembled to the diffuser bya ring clamp 18 of known type. Mounted within the combustion chamber 17is a flame stabilizing device, specifically a generally cylindricalflametube 19 within which the actual combustion and dilution of thecombustion products take place. Air from the compressor is circulatedthrough a space between the walls 17 and 19 and the major part of thissecondary air enters the flame tube through openings in the wallthereof, as is well known. a

Only the forward end of the combustion chamber 17 and the flame tube 19are illustrated, since the details of mese structures are immaterial tothe invention and they may follow Well-known'principles of design. Theoutlets of the flame tubes 19 discharge into the turbine in the usualmanner. The downstream end of the diflfusing passage 11 constitutes theforward part of the combustion chamber, which is continued in thechamber 17. The upstream section or entrance cone of the flame tube isconstituted by a generally conical or diverging shell 22 of heatresistant sheet metal which may be supported in the diffuser by aplurality of legs 23 secured to a flange of the diffuser by studs 24 andnuts. The downstream end of the entrance cone 22 enters Within theupstream end of the flame tube 19, which is ribbed as indicated at 26 tosecure a bearing between the two'members and to provide inlets 27 forcooling air distributed around the circumference. A machine screw 28,threaded into a boss at the forward end of the shell 19, is piloted in ahole in the entrance cone 22 to prevent separation of the parts 19 and22. A slightly tapering sleeve or inner cone 31 is mounted within thenose of the outer cone 22 and fixed thereto by four clips 32 welded tothe two cones. This arrangement provides an annular air inlet 33 to thenose of the combustion cone 22 and a second air inlet through theinterior of the cone 31. The primary combustion air enters through theannular opening 33 and cooling air through the tube 31. Additionalcooling airv may enter through openings in the flame tube 19, as iscustomary.

Liquid fuel for combustion is supplied from any suitable regulatedsource (not shown) through a conduit 36 which is connected by standardtube fittings 37 to a tube- 38 entering the diffuser and passingrearwardly through the inner cone 31. The fittings 37 may be mounted ona.

plate39 fixed to theouter wall 13ofthe-ditfuser by cap are mosteffectively exposed to the gases flowing longi- Eudinally of thecombustion apparatus for best heattrans- The-forward end ofthe-vaporizing coil 42 continues into a tubular ringfuel- -injectionmanifold 44 concentric with the cones 22 and 31 and located ashortdistance downstream fromthe' air inlet 33)" The ring fl is'guidedand"*supp'orted on-*the-inricr-cone31 by a plurality of fingers46"welded tothemanifold 44: A large number of small fuel injection holes47 are drilled in the upstream face of the manifold ring 4-4. T he' sizeand number-of these holes will, of "course," dependupon"thefuelrequiremerits of the'combustion chamber.

The-entrance cone 22-is providedwith an'outwardly extending tube 48,which m'ay be'welded thereto; into which projects the discharge end of atorch ign'iter 50. Thignitefimay be-supported by aplate 51--bolted-tothe out'ebwalllS: Torchigniters are well 'known-,-and the details'of theigniterare immaterialtotheinvention, and-are thereforenotillustrated:The igniter=comprises a fuel spray nozzle or gas jet with means forigniting -the fuel and meansproviding a supply of air underpressureto"pi'ovide a jet offlame into thecombustionchamber: The outlet of'thejet igniter is adjacent the coil 42' so that the igniter-heats thevaporizer.

In operation, the auxiliary'fuel supply to' the igniter 50 is'activatedandthe ignition is energized to providea' flame'jet. When the coil 42has been heated, liquid fuel is introduced through the tube 38, isvaporized in the'coil 42, and injected into the air stream through theorifices 47. The fuel mixes with the air entering through the annularopening 33 and the mixture is ignited by the torch flame.

The jfuel fr om' the manifold 44 burns over the vaporiz er 42, heatingand vaporizing the fuel passing through, and'the'igniter maybe shut oif.Since the fuel is in vapor-form as it enters the air stream, combustiontakes place-immediately after injection without tthe delay-necessa forvaporization of atomized'liquid in the air stream,-

Relatively heavy or non-volatile fuels may be em ployed, sincevaporization is'eifected before injection. The high'pr'essuresrequired'for eflective atomization of liquid fuel are-notrequired with the vapor injection sys min. A pressure of not more thanfifty pounds per'square inch above that in the combustion chamber issufficient.

The torch igniter may bedispened with, if desired, by feedinga gas suchasbutane-or propane, which may be-readily ignited by'aspark-withoutpreheatingor vaporization through the tube 38, and using the flame fromthe manifold 44 to heat the vaporizer. When the vaporizer'is thusheated, the liquid fuel may be fed through the lines 36 and38.

Since the fuel is injected at the extreme forward'end of thefiame*tube;assembly, injected upstream, and in vaporform, burning takesplace at the forward end of the cornbustion space'instcad'of welldownstream as with conventional fluid-spray combustion chambers. Thecombustion apparatus may therefore be decreased in length.

About one-third of-the total air is admitted directly through theopening 33 and the inner cone 31, thus providingi-for a low totalpressure drop as compared-to combustion'chambers in which only arelatively small part ofthe air is admitted at the entrance cone of theflame tube.

The vaporization of the fuel s particularly helpful at extremealtitudeswhere" the density of the airin the 4. combustion-chamber is--low and-rnaintenance of combustion diflicult.

It will be apparent to those skilled in the art from the foregoingdescription that the invention possesses many advantages, andthatthese-advantages may be retained in whole or in part notwithstandingvariations in structure of 'the apparatus employed to effectuate theprinciples of the invention.

The invention is not to be considered-as limited on restricted by thedetailed description. of the preferred embodiment thereof.

In this connection, it may be noted, for example, that the structureshown; with the vaporizingcoil eliminated, is particularly suitediorcombustion'of gaseous fuel. Also, the structure may be readily modifiedfor application to annular combustion casings with annular flame tubesor flame holders therein, while retaining the principles of theinvention. Obviously, the invention is applicable to fuel-burners whichreceivethe gases discharged frorn a turbine'rather than from acompressor, as in reheat burners and afterburners for jet engines.

In certain cases, particularly in afterburners, the fiame tubedownstreamof the entrance portion may be omitted; and theentranceportion'may serve as a flame holder.

Iclairn:

1. Acombustion apparatus comprising; in combination', in combustionchamber structure defining an air passage with' an inlet and an outlet,a flame stabilizing device therein including means defining an inlet forprimary combustion air at the upstream end of the flame stabilizingdevice'and means defining an entrance into the flame stabilizing devicefor additional air downstream from the said inlet, the flame stabilizingdevice portion extending fr'omdhe said inlet to the said entranceincreasing in cross sectionofdo'wnstream, a fuel manifold disposedwithin the-said portion with orifices therein for discharge of fuel"intothe -flame stabilizing device, a fuelheating coil disposed "within saidportion downstream from the manifold and discharging into the manifold,and means for supplying fuelto the heating coil.

2. A combustion apparatus comprising, in -combina-' tion, a combustionchamber structure defining an air passage =with'an inlet and an outlet,at flame stabilizing devicetherein including means defining an inletforprimarycombustion air at the upstream end of the flame stabilizingdevice and meansdefining an entrance into the Iflame stabilizing devicefor additional air downstream from ithe said inlet, the flamestabilizingdevice portion extending from the said inlet to the saidentrance increas= ing in cross section downstream, withinthe' saidportion immediately downstream from the inlet with orifices therei'n'fordischarge of fuel into madame stabilizing'device, a fuel heating coildisposed withinsaid po'rtion'downstream front'the manifold anddischargisgimm the manifold, and means for supplying fuel Ito. the.heating coil.

3. A'eombustion apparatus comprising, in combina-' tion, a-combustionchamber structure defining an air passage' with aninlet and an outlet, aflame stabilizing device therein including. means defining an annularinlet for primary combustion air at the upstream end of the flamestabilizing device and means defining an entrance into the flamestabilizingdevice for additional air downstream from the said inlet,theflame stabilizing device portion extending-from the said inlet to thesaid entranceincreasing in cross section downstream, a tubular'ringfuel'manifold disposed within the said portion adjacent the inlet-withorifices 'therein' for discharge of fuel into the flame stabilizingdevice, a fuel heatingcoil disposedwithin said portion downstream fromthe manifold and discharginginto the'manifold, and means for supplyingfu'el -to the heating coil.

4. A co'mbustion apparatus comprising,'-in combinaa fuel manifolddisposed tion, a combustion chamber structure defining an air passagewith an inlet and an outlet, a flame tube therein comprising an entranceportion with a first air inlet at the end thereof toward the combustionchamber air inlet, a sleeve within the first inlet extending downstreamand defining a second air inlet, a tubular ring fuel injection manifolddisposed around the sleeve adjacent the first air inlet with orificesformed therein for discharge of fuel, and means for supplying gaseousfuel to the manifold.

5. A combustion apparatus comprising, in combination, a combustionchamber structure defining an air passage with an inlet and an outlet, aflame tube therein comprising an entrance portion with a first air inletat the end thereof toward the combustion chamber air inlet, a sleevewithin the first inlet extending downstream and defining a second airinlet, a tubular ring fuel injection manifold disposed around the sleeveadjacent the first air inlet With orifices formed therein for dischargeof fuel, a fuel heating coil arranged around the sleeve downstream fromthe manifold and discharging into the manifold, and means for supplyingfuel to the heating coil.

6. A combustion apparatus comprising, in combination, a combustionchamber structure defining an air passage with an inlet and an outlet, aflame tube therein comprising an entrance portion with a first air inletat the end thereof toward the combustion chamber air inlet, a sleevewithin the first inlet extending downstream and defining a second airinlet, a tubular ring fuel injection manifold disposed around the sleeveadjacent the first air inlet with orifices formed therein for dischargeof fuel, a fuel vaporizing coil arranged around the sleeve downstreamfrom the manifold and discharging into the manifold, means for supplyingfuel to the vaporizing coil, and pilot flame fuel ignition means adaptedto heat the coil.

7. A combustion apparatus comprising, in combination, a combustionchamber structure defining an air passage with an inlet and an outlet, aflame tube therein comprising an entrance portion with an inlet forprimary combustion air at the end thereof toward the combustion chamberair inlet, a sleeve within the said inlet extending downstream anddefining an inlet for cooling air, a tubular ring fuel injectionmanifold disposed around the sleeve adjacent the primary combustion airinlet with orifices formed therein for discharge of fuel, a fuel heatingcoil arranged around the sleeve downstream from the manifold anddischarging into the manifold, and a fuel supply line connected to theheating coil extending into the flame tube through the said sleeve.

References Cited in the file of this patent UNITED STATES PATENTS1,828,784 Perrin Oct. 27, 1931 2,529,506 Lloyd et a1 Nov. 14, 19502,541,900 Williams Feb. 13, 1951 2,552,851 Gist May 15, 1951 2,588,728Hundstad Mar. 11, 1952 2,593,849 Clarke et al. Apr. 22, 1952 2,611,244Clarke et al. Sept. 23, 1952 2,664,703 Whitelaw Ian. 5, 1954

